1. Field of the Invention
The present invention relates to a printing apparatus capable of a double-sided printing, which prints on both surfaces of a print medium, and also to a method for controlling such a printing apparatus.
2. Description of the Related Art
There has been known a printing apparatus capable of performing not only a one-sided printing, which prints on only one surface of a print medium, but also a double-sided printing, which successively prints on both front and back surfaces of the print medium fed from a supply unit. Example constructions of such a printing apparatus are disclosed in Japanese Patent Application Laid-open Nos. 7-323637, 9-327950 and 2002-59598.
Japanese Patent Application Laid-open No. 7-323637 (see FIG. 1 and FIG. 4) discloses a construction of a paper transport path in an ink jet printer or serial printer which allows a print medium to be printed on the back surface following the front surface printing. This official gazette also discloses a correspondence between print data and a print head.
Japanese Patent Application Laid-open No. 9-327950 (see FIG. 1) discloses an ink jet printer in which a paper transport path and a loop-shaped reversing transport path are merged in front of the print head. In this ink jet printer, a print head is installed at a common transport path following the merged portion of the two transport paths. By feeding a print medium past the print head in the forward direction, a one-sided printing is performed on one surface (the front surface). The print medium with one surface printed is then fed in the opposite direction through the reversing transport path for inversion, after which the inverted print medium is again printed now on the other surface (back surface) by the print head.
Japanese Patent Application Laid-open No. 2002-59598 (see FIG. 1) discloses a construction in which a print medium, after being printed on one surface, is transported by a transport belt for front/back inversion and then transported to the print head that prints on the back surface.
Further, Japanese Patent Application Laid-open No. 2003-308183 (see FIG. 18) discloses a printing apparatus control method that processes a plurality of print commands in the printing apparatus capable of double-sided printing.
Here, a common control sequence for a printing apparatus capable of double-sided printing is shown in FIG. 6.
In FIG. 6, when a print job is instructed by a host computer, a check is made to see if a double-sided printing is specified in the job instruction (S601).
When the double-sided printing is specified, a print medium is supplied from a supply unit (S602) and printing is performed on a front surface of the supplied print medium (S603). Then, the sheet that was printed on one surface is fed through the reversing transport path for inversion and the inverted sheet is fed again (S604). It is checked whether there is print data to be printed (S605). If there is print data, the print data is printed on the back surface (S606). The print mediums that have undergone printing are discharged out of the printing apparatus (S607). A check is made to see if there is still print data (S608). If print data exists, another sheet is supplied from the supply unit and is printed first on the front surface (S602-S607).
In a step S605 for checking the presence or absence of print data after the inverted sheet is supplied, if it is decided that data does not exist, the sheet is discharged. The control sequence checks the presence or absence of print data only after the sheet has undergone the front surface printing and the front/back inversion, for the following reason. Suppose that a print medium, after being printed on the front surface, is discharged as is. When sequential pages are successively printed on both surfaces of a plurality of sheets, the order of the page number on the last discharged sheet does not conform with that of the remaining sheets. To prevent this irregularity, the above control sequence is adopted.
Further, in FIG. 6, when a one-sided printing is specified in step S601, a sequence of processing that needs to be executed involves supplying a sheet from the supply unit, printing on one surface and discharging the printed sheet, in that order (S610-S613).
In step S609, when the specified print job is finished, the control program waits until the next print job is received, regardless of whether the last print job specified a double-sided printing or a one-sided printing. When a new print job is received, a check is made to see if the print job specifies the double-sided printing (S601), before starting the printing sequence.
The printing apparatus described in the above patent documents that can perform a double-sided printing are all designed to perform printing and discharging according the printing specification in a print job. Thus, in the above printing apparatus, the double-sided printing function is not fully utilized, giving rise to a problem of increased consumption of print media.
That is, in the printing apparatus described in the above patent documents, even if a double-sided printing is set, a reception of a print job containing only one page of print data results in a sheet discharge immediately following the printing on the front surface. Thus, when a print job for one page of data is received repetitively, as many print mediums printed on one surface as the print jobs are discharged even if the double-sided printing is set, thus consuming the same number of sheets as when the one-sided printing is set.
Japanese Patent Application Laid-open No. 2003-308183, proposes a printing apparatus which accumulates a plurality of print jobs in a memory means in the apparatus, making it possible to ignore the printing specification of each print job in executing a one-sided or double-sided printing. However, since this apparatus needs to accumulate print jobs successively in a memory means, there is a drawback that this arrangement can only be applied to those print jobs that are scheduled in advance.
When, for example, one connects to the Internet and prints relevant information as he or she views various home pages, a double-sided printing is not executed because printing is initiated as print jobs are received irregularly. As a result, a large number of print mediums is consumed, making it impossible to take full advantage of the double-sided printing function. As a memory means to store print jobs, semiconductor memories and hard disks are commonly used. Increasing the capacity of these memory means to accommodate a greater number of print jobs, however, raises another problem of a substantial increase in the cost of the printing apparatus.